Chlorine-modified properties of Ag(111) probed by C2H4, C3H6, C3H5Cl, and CO

Ethene, propene, allyl chloride, and carbon monoxide were used to probe the effects of adding an average of one chlorine atom for every eight Ag atoms of a Ag(111) surface. On the basis of reflection absorption infrared spect roscopy (RAIRS) and temperature-programmed desorption (TPD), this coverage is sufficient to alter the electronic structure of more than 95% of the sur face Ag atoms. For CO, C2H4, and C3H6, TPD peak temperatures increase, indi cating increased adsorbate-substrate bond strength, and vibrational bands a re both red- and blue-shifted compared to the case for adsorption on clean Ag(111). Modes reflecting interactions of pi adsorbate orbitals with the su bstrate are particularly sensitive to the presence of Cl. These changes are attributed to altered electronic structure of Ag atoms, i.e., partially em pty d-band character, induced by the presence of electron-withdrawing Cl. C 3H5Cl is different in that C-Cl bond dissociation to form Cl and C3H5 (ally l) accompanies adsorption on both clean and Cl-covered Ag(111). The influen ce of adsorbed Cl on the thermal chemistry of C3H5 is evident in TPD, and t he adsorption structure taken by adsorbed C3H5 is evident in RAIRS.